The present invention relates to improvements in a reciprocating hydraulic motor. More specifically, the present invention relates to a hydraulic pump coupled to a hydraulic motor employing a reciprocating piston. One use for such motors is to supply slurries of paint, or other coating compositions, to the several spray heads of an airless paint sprayer system.
Hydraulic motors employing reciprocating pistons for airless paint sprayers have been used in the past. One known manufacturer of such a hydraulic motor is The Speeflo Division of Titan Tool, Inc. of Roslyn, N.Y. Other known manufacturers of hydraulic motors for airless paint sprayer systems include Graco, Inc. of Minneapolis, Minn., Durotech Co. of Moorpark, Calif. and Airlessco of Orange, Calif.
Hydraulic pumps can also be used for a variety of other purposes. For example, they can be used in connection with plastic injection molding machines, fork lifts, punch presses, log splitters, and the like. In all such uses, a hydraulically driven device, which is supplied with hydraulic fluid by a hydraulic pump, is preferably moved into position quickly but does its work at the end of the stroke: In such a device, what is required is a high volume of hydraulic fluid at a low pressurexe2x80x94when the device is being moved into positionxe2x80x94and a low volume of hydraulic fluid at a high pressurexe2x80x94when the device does its work.
The function of the hydraulic pump needs to be regulated in all such devices in order to enable the pump to move a high volume of hydraulic fluid at a low pressure and a low volume of hydraulic fluid at a high pressure. The current control circuits for operating such pumps have not been found to be optimum. In current hydraulic pump designs for airless paint sprayers, as the pressure increases, the pump has a tendency to chatter and deliver cyclical amounts of fluid instead of a smooth, steady stream thereof. Most control circuits are also external to the housing of the pump and are thus more susceptible to leakage.
Accordingly, it is desirable to develop a new and improved hydraulic pump which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.
In one embodiment of the present invention, a control circuit for a variable displacement pump is provided.
In this embodiment of the invention, the control circuit comprises a pressure compensator valve in fluid communication with an input of an associated variable displacement pump and a first piston which selectively exerts a first force on a swashplate of the associated variable displacement pump. Also provided is a second piston which selectively exerts a second force on the first piston, and hence on the swashplate of the associated variable displacement pump wherein the second force is in opposition to the first force.
Another embodiment of the present invention relates to a combination pump and control circuit.
In accordance with this embodiment of the invention, a variable displacement pump is provided having a swashplate, an input line and an output line. A pressure compensator valve is in fluid communication with the output line of the variable displacement pump. A first piston has a first end operatively connected to the swashplate wherein the first piston selectively exerts a first force on the swashplate of the variable displacement pump. A second piston is also provided. The second piston selectively contacts the first piston and exerts a second force on a swashplate wherein the second force is in the same direction as the first force. A first biasing element exerts a third force on the swashplate, wherein the third force is in opposition to the first force. A second biasing element is operatively associated with the second piston. The second biasing element exerts a fourth force on the second piston. The fourth force is in opposition to the second force.
In accordance with still another embodiment of the present invention, a combination pump and a control circuit for the pump is provided.
More particularly, in accordance with this embodiment of the invention, the combination comprises a housing and a variable displacement pump having a swashplate, an input line and an output line wherein the variable displacement pump is positioned in the housing. A pressure compensator valve is in fluid communication with the output line of the variable displacement pump. The pressure compensator valve is positioned in the housing. A first piston has a first end operatively connected to the swashplate, wherein the first piston selectively exerts a first force on the swashplate of the variable displacement pump. The first piston is located in the housing. A second piston selectively exerts a second force on the swashplate wherein, the second force is in the same direction as the first force. The second piston is also located in the housing.
One advantage of the present invention is the provision of a new and improved hydraulic pump. The pump is particularly adapted for use with a reciprocating hydraulic motor of an airless paint sprayer system. However, the pump could also be used to power punch presses, log splitters, fork lifts, plastic injection molding machines, and the like.
Another advantage of the present invention is the provision of a hydraulic pump which is regulated by a pressure compensator valve. In this design, a piston is employed to move the swashplate of the pump. The piston is regulated by fluid pressure from the pressure compensator valve.
Still another advantage of the present invention is the provision of a hydraulic pump in which the maximum volume output is controlled by a relationship between a first piston, which adjusts the position of a swashplate of the pump, and a second piston, which adjusts the position of the first piston. By setting the ratio of these two pistons, one can control the fluid pressure at which the two pistons respectively act on the swashplate.
Yet another advantage of the present invention is the provision of a hydraulic pump employing first and second pistons to control the position of a swashplate and a spring mounted adjacent to the second piston to preset the pressure at which the second piston will begin to move in relation to the first piston, thereby controlling the pressure point at which the first piston moves the swashplate and lowers the output volume of the hydraulic pump.
Yet still another advantage of the present invention is the provision of a hydraulic pump which eliminates the hysteresis, or lag time, of the response of a first piston that controls a swashplate position of the hydraulic pump as soon as a pressure drop is detected. This feature decreases xe2x80x9cdead bandxe2x80x9d and the response time of the hydraulic circuit.
A further advantage of the present invention is the provision of a hydraulic pump having a new and improved hydraulic feedback loop to adjust the position of a swashplate of the hydraulic pump. As pressure increases, the effect is to lower the volume demanded of the pump which makes it easier for the pump to meet the demand for hydraulic fluid. To the user, the effect is a smoother, steadier supply of the pumped product, especially at high pressures.
A still further advantage of the present invention is the provision of a hydraulic pump in which pulsations in the output of the hydraulic pump are damped.
A yet further advantage of the present invention is the provision of a hydraulic pump with a control circuit which optimizes the pressurized fluid flow output of a hydraulic pump to a given horsepower input, thus allowing a use of lower horsepower motors to power the hydraulic pump. This reduces the manufacturing cost of the system and also the amount of energy consumed.
An additional advantage of the present invention is the provision of a hydraulic pump which is more compact and lighter in weight for a given output volume of hydraulic fluid and operating pressure.
Yet another advantage of the present invention is the provision of a hydraulic pump with an internal hydraulic control circuit thereby eliminating external piping and possible hazardous leakage points due to external hydraulic connections.
Still other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.